This week's book giveaway is in the OCAJP forum. We're giving away four copies of OCA Java SE 8 Programmer I Study Guide 1Z0-808 and have Jeanne Boyarsky & Scott Selikoff on-line! See this thread for details.
Jar, ear or war files are not compressed in any different way. Some of the contents of a war or ear file are defined by the J2EE spec. You uase a jar file as an archive of java classes, a war file as a packaging unit for web applciations and an ear file as a packaging unit for enterprise applications.